Brownprint fixing composition containing alkali thiosulfate, alkali oxalate, and a surface active wetting agent



Patented Dec. 11, 1951 BROWNPRINT FIXING COMPOSITION CQN TAINING ALKALITHIOSULFATE, ALKALI OXALATE, AND A SURFACE ACTIVE WET- TING AGENT JohnF. Kienast, River Edge, N. .L, assignor to, Keuifel & Esser Company,Hoboken, N. J;,, a. corporation of New Jersey No Drawing. ApplicationJune 18, 1943, Serial No. 100,093

'7 Claims.

This invention relates to a new brownprint fixing composition andprocess. It is a continuation in part of copending application, SerialNo. 597,719, filed June 5, 1945, now abandoned.

Brownprints, also known in the trade as sepia and Van Dyke prints, areproduced by coating on a base material, usually paper, a compositioncontaining a light-sensitive ferric salt of an organic acid, such as thecitrate or oxalate, a soluble silver salt, such as silver nitrate, and asalt that will act as a solvent for the ferrous salts that areeventually formed. This latter salt usually is an alkali salt of apolycarboxylic acid, such as the sodium, potassium, or ammonium salts ofoxalic acid. The most active of these are the oxalates but they have alimited compatability with the silver nitrate and their use in asensitizing coating composition is therefore restricted to relativelysmall amounts when in the same solution.

When used, the sensitized sheet is exposed to actinic light under atracing or the like for the purpose of producing a negative print. Theaction of the light on the exposed areas reduces the trivalent ferriciron to the bivalent ferrous form, which when dissolved in situ by thealkali salt of an organic acid, reduces the silver nitrate to give abrownish image of silver. After exposure it is the custom to wash theprint in water. This wash puts the alkali salt of an organic acid intosolution so that the reaction mentioned may take place. Thereafter thesheet is fixed with a solution of hypo (sodium thiosulfate) to dissolvethe unexposed silver salts, and then given a final wash in water.

Under conditions of unhurried washing and fixing schedules, good printswith stable white areas are readily obtainable from coatings of thistype. However, modern continuous printing machines have such highpowered lights that only very short exposures are required withcorrespondingly curtailed washing and fixing operations. Brownprintsmade in this manner were often found to have lines and other unexposedareas that were discolored or that became discolored after a short time.I have found this discoloration to be due primarily to undissolved ironsalts although silver salts were present in minute amounts.

The present invention provides an improved fixing composition andsolution thereof which will rapidly remove both iron salts, whether inferric or ferrous condition, and silver salts, thus making for apermanent print with clean whites and dense images.

The present invention also provides an im.- proved fixing process inwhich the brownprint is subjected to the new fixing solution.

The improved composition and process are adapted for use according tothe common tub washing and fixing procedure but particular advantagesare derived when they are used on fast continuous printing machines.

In the new fixing composition an alkali oxalate is used together withthe customary hypo (sodium thiosulfate), or other alkali thiosulfate,the alkali oxalate acting in a twofold capacity. It is a powerfulsolvent for undissolved ferric and ferrous iron salts that remain onthey sheet after the first water wash and it also permits the use of anincreased concentration of hypo by retarding the bleaching eifect thatstrong solutions of the latter would ordinarily have on the image. Forexample, by dissolving four ounces of potassium oxalate and four ouncesof hypo (sodium thiosulfate) in one gallon of water, a solution wasobtained which produced, when used in place of the usual hypo fixingsolution, a print having better and more permanent whites with improveddensity and image color.

The fixing composition and process are materially and advantageouslyimproved by also including in the composition a suitable surface activewetting agent, for example, modified sodium lauryl sulfate. The additionof such a wetting agent was found to speed up the solvent and fixingaction of the solution containing hypo and oxalate to such an extentthat the amounts of these. agents could be very materially reduced, e.g., 2 ounces of potassium oxalate plus 2 ounces of hypo, plus 10 gramsof the wetting agent giving similar results to those obtained with 4ounces of potassium oxalate and 4 ounces of hypo per gallon of waterwhen the wetting agent was not included.

While the composition can be prepared in the form of a solution, it isadvantageously prepared in the form of a dry composition, which can bepackaged and shipped and stored and used by adding it to water to formthe fixing solution. In such a composition the hypo is advantageouslyused in the form of the anhydrous salt. The use of ordinary hypocontaining 5 mols. of water of crystallization is not well adapted foradmixture, e. g., with potassium oxalate because of the tendency ofthewater to cause the composition to.

form a sludge. Byusing the anhydrous hypo a satisfactory drycomposition. can readily be prepared.

While sodium and. potassium oxalates may be used, ammonium oxalate isparticularly advantageous for use in the new composition. Althoughammonium oxalate is much less soluble than the potassium salt, itnevertheless has a sufficient solubility for use according to thepresent invention.

The following approximate proportions have been found to be particularlyadvantageous especially for one commercial type of brownprint paper:

Per cent Anhydrous sodium thiosulfate 32 Ammonium oxalate 60 Wettingagent (e. g. modified sodium lauryl sulfate) 8 However, the proportionsmay be varied within the following limits to still produce an effectivefixing composition.

Per cent Anhydrous alkali thiosulfate 20 to 60 Alkali oxalate 80 to 30Wetting agent Oto The proportions which are chosen within the aboveranges may to some extent be dependent on the particular brownprintpaper with which the fixingsolution is intended to be used. This is truebecause commercial brownprint papers do not all have the same proportionof light reducible ferric salt to soluble silver salt and consequently,a composition having a different proportion of ammonium oxalate tosodium thiosulfate than that given in the specific example may besomewhat more effective for certain brownprint papers. It would be arelatively simple matter to determine the best proportions for anyparticular brownprint material.

The dry composition can readily be made and packaged, shipped andstored. In order to make the new fixing solution the composition isdissolved in water in the proportions of e. g., 4 ounces per gallon. Dueto the hydrolysis of the sodium and ammonium salts, the water solutionwill be non-acid and in fact somewhat alkaline in nature.

The procedure for forming brownprints making use of the new fixingsolution may be described as follows:

The brownprint sheet coated with a ferric salt and a soluble silver saltis exposed to light through an original or master to reduce the ferricsalt to a ferrous salt in the light struck areas. The sheet is thenwashed with water to develop the image by allowing the ferrous ions toreduce the soluble silver salt to metallic sil-. ver and by dissolvingthe major portion of the excess salts from the sheet. Then the sheet issubjected to the new fixing solution which fixes the print by removingany remaining silver salts and iron salts from the unexposed areas. Thesheet is then given a final water wash to remove the fixing salt and theiron and silver salts dissolved thereby.

When my solution is used in place of the customary straight hypo fixingsolution a much more rapid and thorough washing out of unexposed saltsis accomplished with the result that cleaner whites are obtained in ashorter time. If the old standard washing and fixing scheduled of 2 to 3minutes first water washing, 1 to 2 minutes in fixing solution and /2 to1 minute of final water wash is followed, the new fixing solution willeffect removal of all unexposed iron and silver salts so that the maskedportions of the print will have the same permanent whiteness as thepaper stock. A

straight hypo fixing solution does not accomplish this resultparticularly on the more retentive, transparentized or "treated papers;hypo being a solvent for the unexposed silver salts only, does notremove the iron salts.

It is an advantage of the present invention that it facilitates the morerapid removal of unexposed iron and silver salts from the brownprintprocess papers. While giving noticeably better results even in the oldfashioned tub washing and fixing procedure, the new composition isparticularly designed and advantageously used, in high speed printingmachines that operate on a relatively short washing and fixing schedule.Another advantage presented by the present invention is the tendency toovercome any bleaching diificulties that arise when a printer attemptsto compensate for the short fixing time by unduly increasing theconcentration of his fixing salts.

The new composition is advantageously prepared in the form of a drycomposition containing anhydrous hypo, the alkali oxalate and wettingagent, mixed together in proper proportions and packaged in packages ofsuitable size, such that, e. g., 1 pound may be dissolved in 4 gallonsof Water or 4 ounces dissolved in 1 gallon of water to give the fixingsolution.

The new fixing solutions can, however, be made by adding each of theindividual agents in suitable proportions to water or by combining twoof the agents together, e. g., the ammonium oxalate and Wetting agent inproper proportions and adding these and the hypo to form the fixingsolution.

The wetting agent used should be one which is compatible with the hypoand oxalate and while different wetting agents can be used the alkalimetal salts of sulfated higher alcohols appear to be particularlyadvantageous.

Thus other dry wetting agents such as hydrocarbon sodium sulfonate,sodium alkyl sulfates, principally sodium lauryl sulfate, iso propylnaphthalene sodium sulfonate, sodium salt of sulfated monoglyceride, andsodium salt of the oleic acid amide of sulfonated ethyl alcohol, may beused. In addition to these, many other wetting agents can be used wherethe original container permits a. fluid condition for the developer orwhere the ingredients are individually added to the solution which is tobe the fixing solution. A typical fluid wetting agent is a solution ofsodium sulfate derivative of 3,9-diethyl tridecanol-G.

From the standpoint of the fixing process it will be seen that thepresent invention enables standard apparatus and procedure to befollowed, using the new fixing solution in place of hypo; and that theprocess is particularly advantageous for use in high speed machines andas a high speed fixing process.

What is claimed is:

1. An anhydrous composition for forming a brownprint fixing solution bythe addition of water thereto consisting essentially of from 20 to 60%of anhydrous alkali thiosulfate, from to 30% of alkali oxalate and from0 to 10% of a dry surfaceactive wetting agent compatible therewith.

2. A composition for forming a brownprint fixing solution by theaddition of water thereto consisting essentially of from 20 to 60% ofsodium thiosulfate, from 80 to 30% of alkali oxalate and from 0 to 10%of a dry surface active wetting agent compatible therewith.

3. An anhydrous composition for forming a brownprint fixing solution bythe addition of water thereto consisting essentially of approximately32% anhydrous sodium thiosulfate, 60% ammonium oxalate and 8% modifiedsodium lauryl sulfate surface active wetting agent.

4. An improved brownprint fixing solution consisting essentially of from20 to 60% of alkali thiosulfate, from 80 to 30% of alkali oxalate andfrom to of a surface active wetting agent compatible therewith dissolvedin water in the proportion of approximately 4 ounces of the specifiedthree ingredients in their indicated proportions to one gallon of water.

5. A composition for forming a brownprint fixing solution by theaddition of water thereto consisting essentially of from 20 to 60% ofanhydrous alkali thiosulfate, from 80 to 30% of alkali oxalate and from0 to 10% of a modified sodium lauryl sulfate surface active wettingagent.

6. A composition for forming a brownprint fixing solution by theaddition of water thereto consisting essentially of from 20 to 60% ofanhydrous alkali thiosulfate, from 30 to 30% of alkali oxalate and from0 to 10% of a surface active wetting agent selected from the groupconsisting of alkali salts of sulfated higher alcohols, hydrocarbonalkali sulfonates, alkali salts of sulfated mono-glycerides and alkalisalts of the oleic acid amide of sulfonated ethyl alcohol.

7. An improved brownprint fixing solution consisting essentially of from20 to 60% of alkali thiosulfate, from 80 to 30% of alkali oxalate andfrom 0 to 10% of a surface active wetting agent selected irom the groupconsisting of alkali salts of sulfated higher alcohols, hydrocarbonalkali sulfonates, alkali salts of sulfated mono-glycerides and alkalisalts of the oleic acid amide of sulfonated ethyl alcohol dissolved inwater in the proportion of approximately 4 ounces of the specified threeingredients in their indicated proportions to one gallon of water.

JOHN F. KIENAST.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Henney and Dudley: Handbook ofPhotography, McGraw-Hill, New York, 1939; page 386 cited.

Clerc: Photography: Theory and Practice," second edition, 1937; pages406 and 408 cited.

Eder: Ausfuholiches Handbuch der Photographic, Band IV, 4 Teil, page 24cited.

1. AN ANHYDROUS COMPOSITION FOR FORMING A BROWNPRINT FIXING SOLUTION BYTHE ADDITION OF WATER THERETO CONSISTING ESSENTIALLY OF FROM 20 TO 60%OF ANHYDROUS ALKALI THIOSULFATE, FROM 80 TO 30% OF ALKALI OXALATE ANDFROM 0 TO 10% OF A DRY SURFACE ACTIVE WETTING AGENT COMPATIBLETHEREWITH.